26 THE LARCH CANKER 
from placing spores in contact with the mucilaginous 
excreta of the Chermes in the spring. , 
A. P. Anderson (1902) gave an account of canker on 
Abies balsamea, which is caused by an allied species, Dasy- 
scypha resinaria. This canker resembles, in most respects, 
that of the larch, and the further details which he provides, 
especially in connexion with resin flow, are for the most 
part equally true for the larch canker. 
Miinch (1909) carried out some interesting experiments 
on the relation between the rate of growth of a canker and 
(i) the air-content of the tissues, (ii) the temperature. He 
cut young shoots (5 cm. broad), which, though cankered, 
were still living, into strips 20-30 cm. long, each with 
a canker. These he dried to varying extents, and found 
that the canker spread much more rapidly in the drier than 
the moister stems. He attributes this to greater air-content, 
but it may also be accounted for by the lessened vitality 
of the tissues induced by drying. He also found that the 
minimum temperature for the growth of the fungus is 
above 0°C., so that it must be incapable of spreading during 
an Alpine winter. ; 
The mycelium of Dasyseypha calycina in the larch stem 
and its effect on the tissues. The hyphae of D yscypha 
calycina have been found in the outer cortex of the leaf 
cushions, the inner cortex, the phloem and xylem, and the 
medullary ray portions of the cambium. 
Its presence in the leaf cushions of uninjured larch stems 
is of no practical importance. No great development of 
Dasyscypha hyphae has been observed in this region ; but 
that there is sufficient nutriment for fungal sustenance in 
these cushions, even when they have been cut off by a cork 
layer, is demonstrated by the fact that fungal pycnidia may 
not infrequently be found growing in them. If the hyphae 
of Dasyscypha obtained a firm hold on the cushion, any 
weak points in the cork armour would be liable to discovery, 
which would put the plant in danger of infection without 
previous wounding ; but there is no direct evidence for this 
ever having taken place. 
